HARRISBURG — Federal regulators proposed a $65,000 fine Tuesday against the owner of a Pennsylvania nuclear plant where security guards routinely napped on the job.

The Nuclear Regulatory Commission announced the fine against Chicago-based Exelon Nuclear after completing a special investigation of the Peach Bottom plant in south-central Pennsylvania.

Multiple guards were "deliberately inattentive" on more than one occasion in a plant "ready room" that serves as a break room, and the incidents were not reported to plant supervisors, the NRC said.

The NRC announced its investigation in September 2007, after a videotape recorded earlier in the year of sleeping guards surfaced. The NRC issued a "white" finding — a low-to-moderate threat — for the incident in February based on the agency's color-coded threat analysis.

Exelon plans to pay the fine, and its monitoring of plant security has improved since the incidents became known, spokeswoman Beth Archer said. The NRC's findings confirmed the results of Exelon's own internal investigation, Archer said.

Exelon ended its security contract with Wackenhut Corp. at Peach Bottom after the videotape surfaced and later replaced the Palm Beach Gardens, Fla.-based company with an in-house security force at all 10 of its nuclear plants.

Exelon is the country's biggest producer of nuclear energy. In addition to Peach Bottom, Exelon owns the Three Mile Island and Limerick plants in Pennsylvania, Oyster Creek in New Jersey, and six plants in Illinois.

Peter Stockton of the Project on Government Oversight, a Washington-based government watchdog group, called the fine "a tap on the wrist."

"The proposed fine probably doesn't even cover the cost of NRC's investigation into the matter," he said.